Recently, radiation has been industrially utilized in extremely wide fields of industry, such as preservation of foods, sterilization of medical equipment, crosslinking of plastics (e.g., electric cables, shrinkable tubes, etc.). Since the exposure dose of radiation greatly influences the intended results of the radiation, it is important to measure the dose to which a material is exposed.
In order to determine the exposure dose, conventional dosimeters, such as a cellulose triacetate film dosimeter, a polymethyl methacrylate dosimeter, a blue cellophane dosimeter, a radiochromic dosimeter, etc., have been used in this field of art. In addition to these dosimeters, a radiation-sensitive (color-changing) tape utilizing polyvinyl chloride has also been used.
Upon using the above cellulose triacetate dosimeter, polymethyl methacrylate dosimeter, and blue cellophane dosimeter, the determination of the exposed dose is complicated by the requirement that the absorbance of the dosimeter be determined using an ultraviolet absorbance meter after exposure.
In the above radiation color-changing tape utilizing polyvinyl chloride, the color changes relatively clearly in the region of an exposed dose of from about 1 to about 10 Mrad (megarad), but in the region of an exposed dose of less than about 1 Mrad or more than about 10 Mrad, the color-changing sensitivity is low and the relationship between the dose and the color change becomes indistinct. Therefore, such a dosimeter cannot be used in fields requiring an exposure dose of about 10 Mrad or more, e.g., crosslinking of plastics (such as electric cables, shrinkable tubes, etc.), and in fields requiring an exposure dose of about 1 Mrad or less, e.g., radiation for foods, although it can be used for an exposure dose of from about 1 to about 10 Mrad.